1. Field of the Invention
The present invention relates to a power train of an automatic transmission. More particularly, the present invention relates to a power train of an automatic transmission that realizes eight forward speeds and one reverse speed by using two double pinion planetary gear sets, one single pinion planetary gear set, four clutches, and two brakes.
2. Description of Related Art
A typical shift mechanism of an automatic transmission utilizes a combination of a plurality of planetary gear sets. A power train of such an automatic transmission that includes the plurality of planetary gear sets changes rotational speed and torque received from a torque converter of the automatic transmission, and accordingly transmits the changed torque to an output shaft.
It is well known that when a transmission realizes a greater number of shift speeds, speed ratios of the transmission can be more optimally designed, and therefore a vehicle can have economical fuel mileage and better performance. For that reason, an automatic transmission that is able to realize more shift speeds is under continuous investigation.
In addition, with the same number of speeds, features of a power train, such as durability, efficiency in power transmission, and size, substantially depend on the layout of the combined planetary gear sets. Therefore, designs for a combining structure of a power train are also under continuous investigation.
A manual transmission that has too many speeds causes inconvenience to a driver. Therefore, the advantageous features of having more shift-speeds are more important in an automatic transmission because an automatic transmission automatically controls the shifting operations.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.